Printed circuit board structure

ABSTRACT

Provided is a printed circuit board structure that needs minimum manufacturing costs and in which there is little possibility that a solder bridge is formed. The printed circuit board structure is formed with via holes for electrically conductively connecting electrically conductive layers of a printed circuit board, and the via holes include a coated via hole with a land coated with solder resist and a non-coated via hole with a land not coated with solder resist, wherein the coated via hole is arranged in a place of the printed circuit board where a solder bridge or a solder ball is highly likely to be generated, and is electrically connected to at least one of the non-coated via hole in parallel.

This application is a new U.S. patent application that claims benefit ofJP 2016-149058, filed on Jul. 28, 2016. The entire content of JP2016-149058 is hereby incorporated by reference.

FIELD

The present invention relates to a printed circuit board structure.

BACKGROUND

It is known to provide conduction among electrically conductive layersof a printed circuit board by forming a through-hole with anelectrically conductive sidewall, which is called a via hole, on theprinted circuit board. The space between via holes formed on a printedcircuit board has been narrowed by reducing the size of electronicequipment, and, in some cases, a solder bridge is formed between thelands (portions of the electrically conductive material of the via holesexposed in a doughnut shape on the surface of the printed circuit board)of adjacent via holes during soldering. In addition, particularly in thevicinity of a portion of the printed circuit board where the heatcapacity is large, in some cases, a solder ball is formed on the land ofa via hole during soldering. When the solder bridge or the solder ballis separated and moved away from the printed circuit board due to somesort of shock or the like and short-circuits the wiring of the printedcircuit board or the lead wires of components after the printed circuitboard is incorporated into electronic equipment, the electronicequipment may malfunction. It is known to prevent the formation of thesolder bridge or the solder ball by applying solder resist on the landsof all via holes that are not used for mounting of a component such thatthe solder does not adhere to the lands of the via holes duringsoldering (see, for example, Patent Document 1).

Related Documents

-   [Patent Document 1] Japanese Laid Open Patent Document No.    H11-154778

SUMMARY

When, however, the solder resist is applied on the land of the via hole,in some cases, the solder resist blocks the opening of the via hole or,even if it does not block the opening, so-called dripping caused by thesolder resist flowing into the through hole of the via hole occurs. Whenthe via hole is blocked or the dripping occurs inside, there is apossibility that an etching solvent or the like used in a printedcircuit board manufacturing process is not fully rinsed off, but remainswithin the via hole, and the via hole is disconnected when the residueof the remaining etching solvent or the like reacts with theelectrically conductive material that covers the side surface of the viahole. The disconnection of the via hole interferes with the conductionbetween the layers of the printed circuit board and the electronicequipment may be eventually malfunction.

The printed circuit board structure according to an embodiment solvesthe aforementioned problem, and it is an object to provide a printedcircuit board structure in which there is little possibility that asolder bridge or a solder ball is formed and there is little possibilitythat malfunction of the electronic equipment due to disconnection of avia hole is generated.

In order to realize the aforementioned object, a printed circuit boardstructure according to the embodiment is formed with via holes forelectrically conductively connecting electrically conductive layers of aprinted circuit board, wherein the via holes include a coated via holewith a land coated with solder resist and a non-coated via hole with aland not coated with solder resist, the coated via hole is arranged in aplace of the printed circuit board where it is highly probable that thesolder bridge or the solder ball is generated, and is electricallyconnected to at least one non-coated via hole in parallel.

In addition, regarding the printed circuit board structure according tothe embodiment, it is preferable that the coated via hole is arranged ina place where a distance between adjacent via holes is equal to or lessthan a predetermined distance, one of the adjacent via holes being thecoated via hole and the other being the non-coated via hole.

In addition, regarding the printed circuit board structure according tothe embodiment, it is preferable that the coated via hole is arranged ina place where a distance from a metal member arranged on the printedcircuit board is equal to or less than a predetermined distance.

In addition, regarding the printed circuit board structure according tothe embodiment, it is preferable to include a first region where anelectronic component is soldered by a flow process or a dip process anda second region protected from solder by a masking jig when soldering isperformed in the first region, wherein the coated via hole is preferablyarranged in a place within the first region where a distance from aboundary with the second region is equal to or less than a predetermineddistance.

In addition, regarding the printed circuit board structure according tothe embodiment, it is preferable that the coated via hole is arranged ona power supply voltage pattern unit of the printed circuit board towhich a power supply voltage is fed.

In addition, regarding the structure of a printed circuit boardaccording to the embodiment, it is preferable that the coated via holeis connected to a ground pattern unit of the printed circuit board to begrounded.

With the structure of the printed circuit board according to theembodiment, it is possible to reduce the possibility that the solderbridge or the solder ball is formed, and it is possible to reduce thepossibility that malfunction of the electronic equipment due todisconnection of a via hole is generated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a partial plan view of a printed circuit board according to afirst embodiment.

FIG. 1B is a partial cross-sectional view of the printed circuit boardillustrated in FIG. 1A.

FIG. 2A is a first view for explaining a distance between a non-coatedvia hole and a coated via hole illustrated in FIGS. 1A and 1B.

FIG. 2B is a second view for explaining a distance between a non-coatedvia hole and a coated via hole illustrated in FIGS. 1A and 1B.

FIG. 3 is a flow chart indicating a coated via hole determinationprocessing for determining the coated via hole illustrated in FIGS. 1Aand 1B.

FIG. 4 is a partial plan view of a printed circuit board according to asecond embodiment.

FIG. 5A is an explanatory view in which a solder ball is formed on theland of a via hole.

FIG. 5B is a view for explaining a distance between a non-coated viahole and a coated via hole illustrated in FIG. 4.

FIG. 6 is a flow chart indicating a coated via hole determinationprocessing for determining the coated via hole illustrated in FIG. 4.

FIG. 7 is a partial plan view of a printed circuit board according to athird embodiment.

FIG. 8 is a view for explaining a distance between a non-coated via holeand a coated via hole illustrated in FIG. 7.

FIG. 9 is a flow chart indicating coated via hole determinationprocessing for determining the coated via hole illustrated in FIG. 7.

FIG. 10A is views illustrating an arrangement example of coated viaholes in which arrangement example, the distance with respect toadjacent non-coated via holes is equal to or less than a solder bridgeformation distance.

FIG. 10B is views illustrating an arrangement example of coated viaholes in which arrangement example, the distance with respect toadjacent non-coated via holes is equal to or less than a solder bridgeformation distance.

FIG. 10C is a view illustrating an arrangement example of coated viaholes in which arrangement example the distance with respect to aboundary is equal to or less than a solder ball formation distance.

FIG. 11A is a view illustrating an example of a state of solder adheredto a via hole in a mounting structure according to a comparativeexample.

FIG. 11B is a view illustrating an example of a state of solder adheredto a via hole of the printed circuit board according to the presentembodiments.

DESCRIPTION OF EMBODIMENTS

A printed circuit board structure according to embodiments is describedwith reference to the drawings below. It should be noted, however, thatthe technical scope of the present invention is not limited to theembodiments, but covers equivalents of the invention stated in theclaims. Regarding the printed circuit board structure according to theembodiments, the via holes include a non-coated via hole with the landnot coated with solder resist and a coated via hole with the land coatedwith solder resist. A via hole the distance from which to an adjacentnon-coated via hole is equal to or less than the distance of theformation of the solder bridge is selectively adopted as a coated viahole so as to minimize the number of coated via holes and minimize thepossibility of the generation of disconnection of the via hole.

(Printed Circuit Board Structure According to the First Embodiment)

FIG. 1A is a partial plan view of a printed circuit board according tothe first embodiment, and FIG. 1B is a partial cross-sectional view ofthe printed circuit board illustrated in FIG. 1A.

A printed circuit board 1 includes a first surface 11 and a secondsurface 12 positioned opposite the first surface 11, and is formed withvia holes 20 and 21 in which the wall surfaces of through-holes 13extending from the first surface 11 to the second surface 12 are coveredwith an electrically conductive material 14, e.g., copper. In addition,in portions where the via hole is exposed on the first surface 11 andthe second surface 12 of the printed circuit board 1, a land 16 wherethe electrically conductive material 14 surrounds the circumference ofthe opening of the via hole in a doughnut shape is formed. An electroniccomponent 30 is soldered on the first surface 11 or the second surface12 of the printed circuit board 1 with solder. Solder resist 15 isapplied on both the first surface 11 and the second surface 12 of theprinted circuit board 1. Regarding the printed circuit board 1, anon-coated via hole and an electronic component, e.g., the electroniccomponent 30, are soldered by the flow process or the dip process.Herein, the flow process indicates a soldering process in which solderstored in a solder bath is jetted and the surface of the circuit boardis washed by the jet, and the dip process indicates a soldering processin which a printed circuit board is dipped in solder stored in a solderbath.

The via holes 20-21 include the non-coated via holes 20 with the lands16 not coated with the solder resist 15 and the coated via holes 21 withthe lands 16 coated with the solder resist 15. A residue 90, e.g., of anetching solvent, can remain in the coated via hole 21.

FIG. 2A is a first view for explaining a distance between the non-coatedvia hole 20 and the coated via hole 21, and FIG. 2B is a second view forexplaining a distance between the non-coated via hole 20 and the coatedvia hole 21.

Regarding the printed circuit board 1, a distance between the coated viahole 21 and the non-coated via hole 20 adjacent to the coated via hole21 is equal to or less than a solder bridge formation distance D₁ wherethe solder for soldering the electronic component 30 forms a solderbridge 18. In other words, when a distance with respect to an adjacentnon-coated via hole 20 is equal to or less than the solder bridgeformation distance D1, such a via hole is selected as the coated viahole 21. Specifically, when a space between adjacent via holes is equalto or less than D1, one of the via holes is selected as the non-coatedvia hole 20 and the other is selected as the coated via hole 21. In oneexample, a via hole the distance from which with respect to an adjacentnon-coated via hole 20 is 0.75 mm or less is selected as the coated viahole 21. When one of adjacent via holes is selected as the coated viahole 21, the solder is not adhered to the land of the via hole 21, sothat the formation of the solder bridge with respect to the land of thenon-coated via hole 20 can be prevented.

Furthermore, the coated via hole 21 is electrically connected to any ofthe non-coated via holes 20 in parallel. Even if the via hole isdisconnected by an etching solvent or the like remaining in thethrough-hole of the coated via hole 21, the non-coated via hole 20connected in parallel maintains the electrical connection, therebyreducing the possibility of malfunction of the electronic equipment.

More preferably, the non-coated via hole 20 and the coated via hole 21are provided on a pattern unit that constitutes a power supply feed lineVDD of the printed circuit board or a pattern unit that constitutes aground line VSS of the printed circuit board. The pattern unitsconstituting the power supply feed line VDD or the ground line VSS isoften grounded with a large number of via holes being electricallyconnected in parallel in order to reduce impedance or ensure morecurrent capacity. In such a portion, even if one or a few coated viaholes 21 are disconnected, the electrical connection is maintained byanother large number of non-coated via holes 20 or the coated via holes21, which are not disconnected, thereby reducing the possibility ofmalfunction of the electronic equipment.

FIG. 3 is a flow chart indicating coated via hole determinationprocessing for determining the coated via hole 21. The processingillustrated in FIG. 3 is executed on each via hole formed on a printedcircuit board by a circuit board design device (e.g., a printed circuitboard design CAD system), which is not illustrated.

First, the circuit board design device judges whether there is apossibility that soldering is performed by the flow process or the dipprocess on a via hole formed on a printed circuit board (S101). When thecircuit board design device judges that there is no possibility thatsoldering is performed by the flow process or the dip process on the viahole formed on the printed circuit board (S101—NO), the processing iscompleted.

When the circuit board design device judges that there is a possibilitythat the soldering is performed on the via hole (S101—YES), the circuitboard design device judges whether there is an adjacent via hole withinthe solder bridge formation distance D₁ where the solder bridge can beformed from the via hole on which the soldering is performed (S102).When the circuit board design device judges that there is no adjacentvia hole within the solder bridge formation distance D1 from the viahole on which the soldering is performed (S102—NO), the processing iscompleted.

When the circuit board design device judges that there is an adjacentvia hole within the solder bridge formation distance D1 (S102—YES), thecircuit board design device judges whether the adjacent via hole withinthe solder bridge formation distance D1 is electrically connected to thenon-coated via hole 20 in parallel (S103). When the circuit board designdevice judges that the adjacent via hole within the solder bridgeformation distance D1 is electrically connected in parallel to thenon-coated via hole 20 (S103—YES), the circuit board design devicedetermines the adjacent via hole as the coated via hole 21 (S104).

When the circuit board design device judges that the adjacent via holewithin the solder bridge formation distance D1 is not electricallyconnected to the non-coated via hole 20 in parallel (S103—NO), thecircuit board design device reviews the arrangement of the via hole(S105). In one example, the circuit board design device arranges the viahole, which has been judged to be not connected to the non-coated viahole 20 in parallel, apart from the non-coated via hole 20 by a distancelarger than the solder bridge formation distance D1.

(Printed Circuit Board Structure According to the Second Embodiment)

FIG. 4 is a partial plan view of a printed circuit board according tothe second embodiment.

A printed circuit board 2 differs from the printed circuit board 1 inthat a metal member 31 is arranged in addition to the electroniccomponent 30. In addition, the printed circuit board 2 differs from theprinted circuit board 1 in that via holes 41 are formed in addition tothe via holes 20-21. Constituent elements of the printed circuit board 2other than the metal member 31 and the via holes 41 are the same as theconstituent elements of the printed circuit board 1, which aredesignated with the same reference numerals, and their detaileddescriptions are omitted.

In one example, the metal member 31 is a heat dissipation fin or ashielding case for electrically shielding a component on the printedcircuit board 2, and is soldered on the first surface 11 of the printedcircuit board 2 by the flow process or the dip process together with theelectronic component 30. In addition, the metal member 31 may bepreliminarily arranged on the printed circuit board 2 independently ofthe electronic component 30 in a different process.

FIG. 5A is an explanatory view in which a solder ball is formed on theland of a via hole, and FIG. 5B is a view for explaining a distancebetween the metal member 31 and the coated via hole 41.

Regarding the printed circuit board 2, a distance between the metalmember 31 and the coated via hole 41 is equal to or less than a solderball formation distance D2 where the solder forms a solder ball 19 onthe land of a via hole. In other words, when a distance between themetal member 31 and the coated via hole 41 is equal to or less than thesolder ball formation distance D2, the via hole is selected as thecoated via hole 41. In one example, when a distance with the metalmember 31 is 1.5 mm or less, the via hole is selected as the coated viahole 41. Because the metal member 31 has a large heat capacity, there isa possibility that, when the electronic component 30 or the like issoldered by the flow process or the dip process, the temperature of theland of a via hole the distance from which to the metal member 31 isequal to or less than the solder ball formation distance D2 is notsufficiently increased, so that the solder is not well spread on theland and the solder ball is formed. When the solder resist is applied toa via hole the distance from which to the metal member 31 is equal to orless than the solder ball formation distance D2, the solder ball can beprevented from being formed on the land of the via hole the distancefrom which to the metal member 31 is equal to or less than the solderball formation distance D2.

Furthermore, as with the first embodiment, the coated via hole 41 iselectrically connected to any of the non-coated via holes 20 inparallel, even if the via hole is disconnected by an etching solvent orthe like remaining in the through-hole of the coated via hole 41, thenon-coated via hole 20 connected in parallel maintains the electricalconnection, thereby reducing the possibility of malfunction of theelectronic equipment, and more preferably, the non-coated via hole 20and the coated via hole 41 are provided on a pattern unit constitutingthe power supply feed line VDD of the printed circuit board and on apattern unit constituting the ground line VSS of the printed circuitboard.

FIG. 6 is a flow chart indicating coated via hole determinationprocessing for determining the coated via hole 41. The processingillustrated in FIG. 6 is executed for each via hole formed on a printedcircuit board by a circuit board design device, which is notillustrated. In addition, the processing of FIG. 6 may be performedcontinuously to the processing indicated in FIG. 3 by the circuit boarddesign device of the first embodiment.

First, the circuit board design device judges whether there is a viahole the distance from which to the metal member 31 is equal to or lessthan the solder ball formation distance D2 where the solder ball can beformed when the soldering is performed with the solder by the flowprocess or the dip process (S201). When the circuit board design devicejudges that there is no via hole the distance from which to the metalmember 31 is equal to or less than the solder ball formation distance D₂(S201—NO), the processing is completed.

When the circuit board design device judges that there is a via hole thedistance from which to the metal member 31 is equal to or less than thesolder ball formation distance D2 (S201—YES), the circuit board designdevice judges whether the via hole is electrically connected to thenon-coated via hole 20 in parallel (S202). When the circuit board designdevice judges that the via hole the distance from which to the metalmember 31 is equal to or less than the solder ball formation distance D2is electrically connected to the non-coated via hole 20 in parallel(S202—YES), the circuit board design device determines the via hole asthe coated via hole 41 (S203).

When the circuit board design device judges that the via hole thedistance from which to the metal member 31 is equal to or less than thesolder ball formation distance D2 is not electrically connected to thenon-coated via hole 20 in parallel (S202—NO), the circuit board designdevice reviews the arrangement of the via hole (S204). In one example,the circuit board design device arranges the via hole, which has beenjudged to be not connected to the non-coated via hole 20 in parallel,apart from the metal member 31 by a distance larger than the solder ballformation distance D2.

(Printed Circuit Board Structure According to the Third Embodiment)

FIG. 7 is a partial plan view of a printed circuit board according tothe third embodiment.

A printed circuit board 3 differs from the printed circuit board 1 inthat the printed circuit board 3 includes a first region 51 in which anelectronic component is soldered by the flow process or the dip processand a second region 52 in which an electronic component is soldered by areflow process. The reflow process indicates a soldering process inwhich solder paste is printed on a printed circuit board and is heatedwith an electronic component being arranged on the printed solder paste.A boundary 50 to be descried below is present between the first region51 and the second region 52. Preferably, a line indicating the boundary50 is printed by silkscreen printing or the like. The printed circuitboard 3 differs from the printed circuit board 1 in that an electroniccomponent 32 is arranged in addition to the electronic component 30. Inaddition, the printed circuit board 3 differs from the printed circuitboard 1 in that via holes 61 are formed in addition to the via holes20-21. Constituent elements of the printed circuit board 3 other thanthe electronic component 32 and the via holes 61 are the same as theconstituent elements of the printed circuit board 1, which aredesignated with the same reference numerals, and their detaileddescriptions are omitted.

The electronic component 32 is soldered by the reflow process and isarranged in the second region 52. Then, the electronic component 30 issoldered by the flow process or the dip process and is arranged in thefirst region 51. The reflow process is suitable for soldering asmall-sized component, and the flow process or the dip process issuitable for soldering a large-sized component. Using such techniquesenables adoption of a suitable soldering method when a small-sizedcomponent and a large-sized component are arranged together on oneprinted circuit board. Furthermore, when the electronic component 30 issoldered by the flow process or the dip process and is arranged in thefirst region 51, the second region 52 is protected by being covered witha metallic masking jig so that the electronic component 32, which ispreliminarily soldered by the reflow process and is arranged in thesecond region 52, is not removed by being washed by the solder in theflow process or the dip process. In this case, the boundary 50 is a lineindicating a range where the metallic masking jig contacts the printedcircuit board 3.

FIG. 8 is a view for explaining a distance between the boundary 50 andthe coated via hole 61.

Regarding the printed circuit board 3, a distance between the boundary50 and the coated via hole 61 is equal to or less than the solder ballformation distance D2 where the solder for soldering the electroniccomponent 30 forms the solder ball 19. In other words, when a distancebetween the boundary 50 and the coated via hole 61 is equal to or lessthan the solder ball formation distance D2, the via hole is selected asthe coated via hole 61. In one example, when a distance with theboundary 50 is 1.5 mm or less, the via hole is selected as the coatedvia hole 61. As described above, the boundary 50 indicates a range wherethe metallic masking jig contacts the printed circuit board 3 when theelectronic component, e.g., the electronic component 30, arranged in thefirst region 51 is soldered by the flow process or the dip process.Because the metallic masking jig has a large heat capacity, there is apossibility that, when the electronic component 30 or the like issoldered by the flow process or the dip process, the temperature of theland of the via hole the distance from which to the boundary 50 is equalto or less than the solder ball formation distance D2 is notsufficiently increased, so that the solder is not well spread on theland and the solder ball is formed on the land. When the solder resistis applied over a via hole the distance from which to the boundary 50 isequal or less than the solder ball formation distance D2, the solderball can be prevented from being formed on the land of the via holelying within the solder ball formation distance D2.

Furthermore, as with the first embodiment, the coated via hole 61 iselectrically connected to any of the non-coated via holes 20 inparallel, even if the via hole is disconnected by an etching solvent orthe like remaining in the through-hole of the coated via hole 61, thenon-coated via hole 20 connected in parallel maintains the electricalconnection, thereby reducing the possibility of malfunction of theelectronic equipment, and more preferably, the non-coated via hole 20and the coated via hole 61 are provided on a pattern unit constitutingthe power supply feed line VDD of the printed circuit board and on apattern unit constituting the ground line VSS of the printed circuitboard.

FIG. 9 is a flow chart indicating coated via hole determinationprocessing for determining the coated via hole 61. The processingillustrated in FIG. 9 is executed on each via hole formed on a printedcircuit board by a circuit board design device, which is notillustrated. In addition, the processing of FIG. 9 may be performedcontinuously to the processing illustrated in FIG. 3 or FIG. 6 by thecircuit board design device of the first embodiment or the secondembodiment.

First, the circuit board design device judges whether there is a viahole the distance from which to the boundary 50 is equal to or less thanthe solder ball formation distance D2 where the solder ball can beformed when the soldering is performed with the solder by the flowprocess or the dip process (S301). When the circuit board design devicejudges that there is no via hole the distance from which to the boundary50 is equal to or less than the solder ball formation distance D2(S301—NO), the processing is completed.

When the circuit board design device judges that there is a via hole thedistance from which to the boundary 50 is equal to or less than thesolder ball formation distance D2 (S301—YES), the circuit board designdevice judges whether the via hole is electrically connected to thenon-coated via hole 20 in parallel (S302). When the circuit board designdevice judges that the via hole the distance from which to the boundary50 is equal to or less than the solder ball formation distance D2 iselectrically connected to the non-coated via hole 20 in parallel(S302—YES), the circuit board design device determines the via hole asthe coated via hole 61 (S303).

When the circuit board design device judges that the via hole thedistance from which to the boundary 50 is equal to or less than thesolder ball formation distance D2 is not electrically connected to thenon-coated via hole 20 in parallel (S302—NO), the circuit board designdevice reviews the arrangement of the via hole (S303). In one example,the circuit board design device arranges the via hole, which has beenjudged to be not connected to the non-coated via hole 20 in parallel,apart from the boundary 50 by a distance larger than the ball formationdistance D2.

In the description above, the electronic component 32 arranged in thesecond region 52 is soldered by the reflow process. However, the methodof arranging the electronic component 32 to be arranged in the secondregion 52 is not limited thereto, but other soldering methods (the flowmethod and the dip method) or other joining methods (bonding withelectrically conductive paste or the like) may be used. In short, theprinted circuit board structure of the present embodiments may beadopted insofar as a technique of protecting the second region 52 with amasking jig is adopted so that the solder does not enter the secondregion 52 where the electronic component 32 is already arranged when thesoldering is performed in the first region 51 by the flow process or thedip process.

FIG. 10 is a view illustrating an example of the printed circuit boarddescribed in the first embodiment to the third embodiment. FIG. 10A is afirst view illustrating an arrangement example of the coated via holes21, FIG. 10B is a second view illustrating an arrangement example of thecoated via holes 21, and FIG. 10C is a view illustrating an arrangementexample of the coated via holes 61. In FIG. 10A, the coated via holes 21are indicated by square marks, in FIG. 10B, the coated via holes 21 areindicated by circular marks, and in FIG. 10C, the coated via holes 61are indicated by triangular marks.

In the example illustrated in FIG. 10, the printed circuit board is aglass epoxy substrate, which is also called an FR-4 (Flame RetardantType 4). The printed circuit board has a thickness of 1.6 mm, and thevia holes formed on the printed circuit board have a diameter of 0.3 mm.The solder for soldering the electronic component by the flow process orthe dip process is Sn—3.0% Ag—0.5% Cu (tin 96.5%, silver 3%, copper 0.5%(lead free).

The temperature of the solder in the solder bath used when the solderingis performed in the first region 51 by the flow process or the dipprocess is 320° C.±5° C. Soldering time for soldering by the flowprocess or the dip process is about six seconds or less althoughtemperature increase time, fillet formation time and the like vary withconditions such as the size and the shape of an electronic component,and the size, the material and the shape of a terminal.

The coated via holes 21 illustrated by square marks in FIG. 10A are viaholes the distance from which to adjacent non-coated via holes 20 is0.75 mm or less and which are connected to the power supply feed lineVDD. The coated via holes 21 illustrated by circular marks in FIG. 10Bare via holes the distance from which to adjacent non-coated via holes20 is 0.75 mm or less and which are connected to the ground line VSS.The coated via holes 61 indicated by triangular marks in FIG. 10C arevia holes the distance from which to the boundary 50 is 1.5 mm or lessand which are connected to the ground line VSS.

The distance between the coated via hole 21 and the non-coated via hole20, and the distance between the boundary 50 and the coated via hole 61were determined based on an experiment in which the soldering time waschanged with respect to various types of components. The minimum valueof the soldering time is minimum time that can ensure the connectionstrength of the solder, and the upper limit value of the soldering timeis six seconds.

(Technical Effect of the Printed Circuit Board Structure According tothe Embodiments)

Regarding the printed circuit board structure according to theembodiments, the solder resist is applied over a via hole the distancefrom which to an adjacent via hole is equal to or less than the solderbridge formation distance where the solder bridge is formed and on whichthe soldering is not performed. Regarding the printed circuit boardstructure according to the embodiments, because the solder resist isapplied over a via hole the distance from which to an adjacent via holeis equal to or less than the solder bridge formation distance and onwhich the soldering is not performed, the formation of the solder bridgecan be prevented during the soldering by the flow process or the dipprocess.

FIG. 11A is a view illustrating an example of a state where the solderis adhered to a via hole in a mounting structure according to acomparative example, and FIG. 11B is a view illustrating an example of astate where the solder is adhered to a via hole in a printed circuitboard according to the present embodiment. In the example illustrated inFIG. 11A, the solder resist is not applied over the via hole on whichthe soldering is not performed, and in the example illustrated in FIG.11B, as in the case of the printed circuit boards 1 to 3, the non-coatedvia hole and the coated via hole are arranged.

In the example illustrated in FIG. 11A, because the solder is adhered toa land exposed portion during the soldering by the flow process or thedip process, the solder bridge or the solder ball can be formed. Incontrast, in the example illustrated in FIG. 11B, because unnecessarysolder is not adhered during the soldering by the flow process or thedip process, there is no possibility that the solder bridge or thesolder ball is formed.

In addition, regarding the printed circuit board structure according tothe embodiments, the solder resist is applied over a via hole thedistance from which to a metal member is equal to or less than thesolder ball formation distance where the solder ball is formed and onwhich the soldering is not performed. Regarding the printed circuitboard structure according to the embodiments, because the solder resistis applied over a via hole the distance from which to a metal member isequal to or less than the solder ball formation distance and on whichthe soldering is not performed, the formation of the solder ball on theland of the via hole can be prevented during the soldering by the flowprocess or the dip process.

In addition, regarding the printed circuit board structure according tothe embodiments, the solder resist is applied over a via hole thedistance of which with respect to the boundary with respect to theregion where the soldering is performed by the reflow process and onwhich the soldering is not performed. In addition, in the printedcircuit board structure according to the embodiments, the solder resistis applied to a via hole the distance from which to the boundary withthe region where the soldering is performed by the reflow process isequal to or less than the solder ball formation distance where thesolder ball is formed and on which the soldering is not performed.Regarding the printed circuit board structure according to theembodiments, because the solder resist is applied over a via hole thedistance from which to the boundary is equal to or less than the solderball formation distance and on which the soldering is not performed, theformation of the solder ball due to influences of a masking jig can beprevented during the soldering by the flow process or the dip process.

In addition, regarding the printed circuit board structure according tothe embodiments, the coated via hole, which is coated with the solderresist, is electrically connected to any of the non-coated via holes,which are not coated with the solder resist, in parallel. Regarding theprinted circuit board structure according to the embodiments, becausethe coated via hole is connected to the non-coated via hole, even whenthe disconnection occurs in the coated via hole, because an electricsignal is transmitted and received via the non-coated via hole, there isno possibility that the function of the printed circuit board is lost.

In addition, regarding the printed circuit board structure according tothe embodiments, because any of the coated via holes is connected to thepower supply voltage line connected to the non-coated via hole, evenwhen the disconnection occurs in the coated via hole, a power supplyvoltage can be fed via the non-coated via hole.

In addition, regarding the printed circuit board structure according tothe embodiments, because any of the coated via holes is connected to theground line connected to the non-coated via hole, even when thedisconnection occurs in the coated via hole, grounding can be made viathe non-coated via hole.

The via holes 20 and 41 are arranged on the printed circuit board 2, andthe via holes 20 and 61 are arranged on the printed circuit board 3.However, the via holes 41 and 61 may be arranged on the printed circuitboard according to the embodiments.

What is claimed is:
 1. A printed circuit board structure comprising: aplurality of via holes for electrically conductively connecting aplurality of electrically conductive layers of a printed circuit board,the plurality of via holes including a coated via hole with a landcoated with solder resist and a non-coated via hole with a land notcoated with solder resist, wherein the coated via hole is arranged in aplace of the printed circuit board where a solder bridge or a solderball is highly likely to be generated, and is electrically connected toat least one of the non-coated via hole in parallel.
 2. The printedcircuit board structure according to claim 1, wherein the coated viahole is arranged in a place where a distance between adjacent via holesis equal to or less than a predetermined distance, one of the adjacentvia holes is a coated via hole and an other of the adjacent via holes isa non-coated via hole.
 3. The printed circuit board structure accordingto claim 1, wherein the coated via hole is arranged in a place where adistance from a metal member arranged on the printed circuit board isequal to or less than a predetermined distance.
 4. The printed circuitboard structure according to claim 1, comprising: a first region inwhich an electronic component is soldered by a flow process or a dipprocess; and a second region protected from solder by a masking jig whensoldering is performed in the first region, wherein: the coated via holeis present in the first region and arranged in a place where a distancefrom a boundary with the second region is equal to or less than apredetermined distance.
 5. The printed circuit board structure accordingto claim 1, wherein the coated via hole is arranged on a power supplyvoltage pattern unit of the printed circuit board to which a powersupply voltage is fed.
 6. The printed circuit board structure accordingto claim 1, wherein the coated via hole is connected to a ground patternunit of the printed circuit board to be grounded.